Thomas Hüttl at ASM explores the advances of power electronic module SMT placement and just what is making SMT systems an increasingly viable option
With their large, unwieldy modules, plugs and connectors with press-fit or THT technology, power electronics pose special challenges for SMT machines. As it turns out, the degree of SMT placement in power electronics is more a question of cost-effectiveness than of the SMT placement equipment’s capabilities.
On power electronics modules large odd-shaped components, lots of connectors and mechanical parts crowd each other on relatively large and heavy boards. Press-fit and through-the-hole technologies are widespread. Nevertheless, modern placement machines are well-prepared for the special requirements of power electronics.
Many power electronics boards feature metallic cores and special large-mass areas. They are significantly heavier than regular PCBs. This does not normally pose problems for conveyor systems that are optionally equipped for PCBs weighing up to 5 kilograms. What is important, however, is the ability to adapt the conveyor systems’ acceleration and deceleration behaviour via the special profiles.
To make large connectors SMT-capable without jeopardising their mechanical stability, they are often equipped with board locks or interlocks. When an SMT machine places them, it must exert a force of up to 70N – a force that premium placement machines can deliver, at least optionally. Placement force measurement and board support techniques, on the other hand, are areas where the wheat is separated from the chaff. In response SIPLACE SPS (Smart Pin Support) from ASM Assembly Systems is designed to offer automated pin placement. With this system, users can determine the ideal pin positions for supporting large boards already in the placement program. When the first board enters the machine, the system positions the pins automatically, a process which prevents errors and saves time.
For many power electronics components, trays and linear feeders are the preferred supply modules. In view of the large component diversity in the field, the development of future feeder standards is unlikely, and special designs will remain the only solution in many cases. That’s why it is so important for machine manufacturers to support openness and flexibility. This, for example, offers a Feeder Development Kit (FDK) for manufacturers of third-party feeder modules.
The FDK includes not only the associated interface specification and timing diagrams, but support and test services from the Application Centre.
Feeder manufacturers can thus adapt their OSC models to the respective machines and make sure that components are supplied in a reliable manner. With a SIPLACE CA, components can even be taken directly from wafer magazines with no special process.
Use of component grippers
With grippers, these machines can place even the most unusual OSCs. Various gripper constructions meet diverse requirements regarding holding and placement forces (gripping from the outside, spreading from the inside, omitting sensitive areas, etc.). There are nevertheless important differences in the approaches of different equipment makers. For example, these grippers operate with the same air pressure as standard nozzles. This makes it possible to switch out grippers like vacuum nozzles and store them in the same nozzle magazines. The benefit: While a permanently mounted gripper would block a placement head, magazines from this product range can use the placement head for standard components after the usually small number of OSCs has been placed with the gripper.
Another idea the company has come up with is its Multigripper Kit, with which electronics manufacturers can build their own special grippers, this is especially useful when they are needed right away for prototypes or small lots and having special models manufactured would take too long.
Air pressure compatibility and the Multigripper Kit of this particular system place focus on a critical factor concerning production of power electronics: its cost-effectiveness. In purely technical terms, virtually any equipment maker’s machine is able to handle the job; the big differences lie in speed and efficiency.
To stay with the gripper example: If a permanently mounted gripper blocks a placement head for only a few special components, the impact on the SMT line’s overall performance and productivity may be severe.
The more effective special processes have been integrated into a placement system, the more efficient it will operate. That’s why it makes sense to have gluing, fluxing, pin-in-paste, bare-die placements and the placing of connectors with grid-locks performed by the same machine wherever possible.
The company has also recently introduced a Glue Feeder in this rage. The new adhesive dispenser can be installed just like a feeder anywhere on the line.
Can power electronics and odd-shaped components be processed by SMT machines? Here the core question should be: when is it cost-effective? And the answer depends on product, component and process details. Some odd-shaped components can be easily placed with appropriately flexible placement machines. If the share of OSCs rises, however, it may make more sense to employ a special placement system for them.
As placement machines become more powerful and flexible, producing power electronics via an automated SMT process becomes more and more attractive. But the speed advantage for individual OSCs which were placed manually or via a special process may be wiped out by the negative side effects on the placement efficiency of other components. It therefore makes sense to carefully analyse or simulate the cycle and throughput times before making a decision.
Thomas Hüttl is Product Marketing Manager at ASM Assembly Systems
ASM Assembly Systems